When a horse goes lame, more and more often X-rays are taken to aid in diagnosis. When enlarged foraminae nutritiae are detected in the navicular bone, navicular syndrome is usually the diagnosis.The size and shape of these cavities varies in all horses. These variations are attributed to a number of causes, from age to immunological deficiencies. However, more recent studies have proven that there exists no direct relationship between the shape of the cavities and clinical lameness. However, what is proven 100% of the time is that "navicular" horses ALL have long, underslung heels and bars which contact the ground (or shoe) even when non-weighbearing. This causes a lever action into the sole and results in bruising and tearing in the area of the bars under the navicular bone. To escape the pain, the horse tries to put less pressure on the heel, and therefore more on the toe; the angle between the coffin bone and middle phalanx decreases, causing the navicular bone to close off the Aa. digitales. This results in congestion above this point and enlargement of arteries.
Lameness disappears after elimiation of this hoof form and restoration of the natural, flat shape.
No relapse has ever been noted.
This leads to the conclusion that the so-called "navicular syndrome" has its cause in an unnatural hoof form, more specifically in excessively long heels and bars, which put pressure into the navicular region and cause inflammation (pain) of the corium in this area. Since, below the region of congestion, blood flow and therefore nerve action is reduced, at first there is little or no pain with this situation. Only after increased inflammation, which returns blood to the affected area, is lameness noted.The belief that steep hooves are proper (perhaps caused by the mistaken idea that they relieve the flexor tendons) therefore causes many cases of navicular. It is not navicular syndrome which is hereditary, but ignorance of the proper hoof shape.